1. Field of the Invention
The present invention relates to a thin-film magnetic head, and more particularly to an inductive thin-film magnetic head whose magnetic core has large permeability and is excellent in magnetic stability.
2. Description of the Related Art
As the track pitch of magnetic disc drive has been made narrow, it has become very difficult to fabricate a thin-film magnetic head for high-density recording. For example, in order to develop a thin-film magnetic head having a track width of about 15 .mu.m, it is necessary to put the magnetostriction constants of its magnetic core in a narrower range, as compared with the magnetic core of a conventional thin-film magnetic head having a track width of 25 to 30 .mu.m. When the magnetostriction constants of the magnetic core are restricted within the narrower range, a process margin becomes very small, and thus some trouble may arise in mass producing a thin-film magnetic head.
The read and write characteristics of a thin-film magnetic head are greatly dependent upon the magnetic characteristics of a magnetic core included in the magnetic head. An inductive thin-film magnetic head is used in a high-frequency range, and hence the magnetic core of this magnetic head has high magnetic permeability in the high-frequency range, as mentioned below. That is, a magnetic core having uniaxial magnetic anisotropy is formed so that the easy axis of magnetization is parallel to the direction of the track width of the magnetic head, and a magnetic field is applied to the magnetic core in the direction of the hard axis of magnetization, to cause the reversion of magnetization by the revolution (namely, rotation) of magnetization, thereby increasing the magnetic permeability of the magnetic core in the high-frequency range. In such a thin-film magnetic head, however, the easy axis of magnetization is rotated by the magnetoelastic effect based upon a stress applied to the magnetic core and the magnetostriction constant of a magnetic film for forming the magnetic core, and thus it is impossible to maintain the predetermined magnetic anisotropy. Accordingly, the read and write characteristics of the magnetic head are degraded. As regards the above problem, a Japanese patent application (unexamined publication No. 55-101124) discloses that it is preferred to form a magnetic core of a magnetic film having a negative magnetostriction constant, since a tensile stress is applied to the magnetic core in a direction perpendicular to the direction of the track width of the magnetic core. Further, a Japanese patent application (unexamined publication No. 58-80120) discloses that a complicated stress is applied to a magnetic core, and hence it is preferred to form the magnetic core of a magnetic film having a magnetostriction constant whose absolute value is not greater than 1.times.10.sup.-6. Similar techniques are disclosed in a U.S. patent application Ser. No. 460,658 filed on Jan. 24, 1983, now U.S. Pat. No. 4,626,947 which is incorporated herein by reference. According to the inventors' experiments, however, it has been confirmed that in a case where a magnetic core is formed of a magnetic film having a negative magnetostriction constants whose absolute value is large, when a tensile stress is applied to the magnetic core, the permeability thereof is reduced, and the read and write characteristics of a magnetic head including the (above-mentioned) magnetic core is degraded. Further, it has been confirmed by experiments that in a case where a magnetic head has a small track width suitable for high density recording and a magnetic core included in the magnetic head is formed of a magnetic film having a positive magnetostriction constant, even when the positive magnetostriction constant is less than 1.times.10.sup.-6, the magnetic core is magnetically unstable, and thus the noise level in a signal reproduced by the magnetic head is high.
It is very difficult to control the magnetostriction constants of a magnetic film within a narrow range and to control a stress applied to the magnetic film Moreover, such processing will make the process margin small, and thus may cause some trouble in mass producing a magnetic head including the magnetic film.